Hide herdr's outer pane frame like tmux

config/herdr/config.toml

@@ -70,8 +70,9 @@ next_workspace = ["prefix+shift+n", "alt+down"]
 [ui]
 accent = "blue"
 
-# tmux drew single-line dividers between adjacent panes
+# tmux drew single-line dividers between adjacent panes and no outer frame
 pane_gaps = false
+pane_outer_borders = false
 
 # tmux had no scrollbar column beside its panes
 pane_scrollbars = false